Leptin directly stimulates parathyroid hormone secretion

Association Between Renal Sinus Fat and Cardiometabolic and Renin-Angiotensin System Parameters in Primary Aldosteronism

Context

Renal sinus fat (RSF) accumulation is associated with cardiometabolic diseases, such as obesity, diabetes, hypertension, and chronic kidney disease. However, clinical implications of RSF in primary aldosteronism (PA) remain unclear.

Objective

We aimed to investigate relationships between RSF volume and key cardiometabolic and renin-angiotensin system (RAS) parameters in PA patients and clarify the differences in these relationships between unilateral and bilateral subtypes.

Methods

We analyzed data obtained from well-characterized PA patients that involved 45 unilateral (median age: 52 years; 42.2% men) and 92 bilateral patients (51 years; 42.4% men).

Results

RSF volume normalized by renal volume (RSF%) was greater in the unilateral group than in the bilateral group (P < .05). RSF% was greater in men than in women (P < .05). RSF% positively correlated with parameters related to cardiometabolic risk, including age, body mass index, visceral fat volume, creatinine, triglycerides/high-density lipoprotein cholesterol ratio, uric acid, fasting glucose, and C-reactive protein regardless of PA subtypes (all P < .05). Intriguingly, RSF% positively correlated with plasma aldosterone concentration (PAC), aldosterone-to-renin ratio, and intact parathyroid hormone (iPTH) (all P < .05) in bilateral patients but did not correlate with RAS parameters and even showed an opposite trend in unilateral patients. In subgroup analyses by sex, these distinctions became more evident in women. After adjustment for potential confounders, RSF% remained positively correlated with PAC and iPTH in bilateral patients.

Conclusion

Our results indicate that RSF accumulation is involved in cardiometabolic dysfunction associated with PA. However, there were distinct correlations between RSF volume and RAS parameters according to sex and PA subtypes.

Primary hyperparathyroidism in young patients is associated with metabolic disorders: a prospective comparative study

BACKGROUND

Components of metabolic syndrome can be observed in patients with primary hyperparathyroidism (PHPT). The link between these disorders remains unclear due to the lack of relevant experimental models and the heterogeneity of examined groups. The effect of surgery on metabolic abnormalities is also controversial. We conducted a comprehensive assessment of metabolic parameters in young patients with PHPT.

METHODS

One-center prospective comparative study was carried out. The participants underwent a complex biochemical and hormonal examination, a hyperinsulinemic euglycemic and hyperglycemic clamps, a bioelectrical impedance analysis of the body composition before and 13 months after parathyroidectomy compared to sex-, age- and body mass index matched healthy volunteers.

RESULTS

45.8% of patients (n = 24) had excessive visceral fat. Insulin resistance was detected in 54.2% of cases. PHPT patients had higher serum triglycerides, lower M-value and higher C-peptide and insulin levels in both phases of insulin secretion compared to the control group (p < 0.05 for all parameters). There were tendencies to decreased fasting glucose (p = 0.031), uric acid (p = 0.044) and insulin levels of the second secretion phase (p = 0.039) after surgery, but no statistically significant changes of lipid profile and M-value as well as body composition were revealed. We obtained negative correlations between percent body fat and osteocalcin and magnesium levels in patients before surgery.

CONCLUSION

PHPT is associated with insulin resistance that is the main risk factor of serious metabolic disorders. Surgery may potentially improve carbohydrate and purine metabolism.

New concepts in regulation and function of the FGF23

In comparison to the regulation of calcium homeostasis, which has been widely studied over the last several decades, phosphate homeostasis is little understood. The parathyroid hormone (PTH)/vitamin D axis has traditionally been used as a conceptual framework for understanding mineral metabolism. Recently, the fundamental regulator of phosphate homeostasis, fibroblast growth factor 23 (FGF23), which is produced by osteocytes and is involved in the hormonal bone-parathyroid-kidney axis, has attracted more attention. The secretion of FGF23 is controlled by diet, serum phosphate levels, PTH, and 1,25(OH)2 vitamin D. FGF-23, the FGF receptors and the obligate co-receptor α-Klotho work in concert to affect FGF-23 actions on targeted organs. Despite all efforts to investigate pleotropic effects of FGF23 in various endocrine organs, many aspects of the regulation and functions of FGF23 and the exact crosstalk among FGF23, serum phosphate, calcium, PTH, and vitamin D in the regulation of mineral homeostasis remain unclear; much efforts need to be established before it can be moved toward therapeutic applications. In this regard, we provide a brief overview of the novel findings in the regulation and function of FGF23 and refer to related questions and hypotheses not answered yet, which can be a window for future projects. We also focus on the current knowledge about the role of FGF23 obtained from our researches in recent years.

Leptin Enhances Hepatic Fibrosis and Inflammation in a Mouse Model of Cholestasis

Leptin is an adipokine with roles in food intake and energy metabolism through its actions on neurons in the hypothalamus. The role of leptin in obesity and cardiovascular disorders is well documented. However, its influence on liver conditions such as cholestasis is poorly understood. The effects of exogenous leptin and leptin-neutralizing antibody on biliary hyperplasia, hepatic fibrosis, and inflammation in the multidrug resistance protein 2 knockout (Mdr2KO) mouse model of cholestasis were assessed by quantifying markers specific for cholangiocytes, activated hepatic stellate cells (HSCs), and cytokines. Serum and hepatic leptin were increased in Mdr2KO mice compared with FVB/NJ (FVBN) controls, and exogenous leptin enhanced biliary hyperplasia and liver fibrosis in Mdr2KO and FVBN mice. Leptin administration increased hepatic expression of C-C motif chemokine ligand 2 and IL-6 in Mdr2KO mice. In contrast, leptin-neutralizing antibody reduced intrahepatic bile duct mass and decreased HSC activation in Mdr2KO mice compared with FVBN controls. Sex-related differences were noted, with female Mdr2KO mice having more leptin than males. In cholangiocytes and LX2 cells in vitro, leptin increased phosphorylated Akt and stimulated cell proliferation. Leptin receptor siRNA and inhibitors of Akt phosphorylation impaired leptin-induced cell proliferation and proinflammatory cytokines. The current data suggest that leptin is abnormally increased in cholestatic mice, and excess leptin increases ductular reaction, hepatic fibrosis, and inflammation via leptin receptor-mediated phosphorylation of Akt in cholangiocytes and HSCs.

The relationship between the level of vitamin D, leptin and FGF23 in girls and young women with polycystic ovary syndrome

Polycystic ovary syndrome is an endocrinopathy that mainly affects adolescent girls and young women of childbearing age. In girls, the presence of clinical and biochemical symptoms of hyperandrogenism should be particularly considered. The role of vitamin D deficiency in insulin resistance, inflammation, dyslipidemia, and obesity, i.e. in diseases associated with PCOS, has been investigated, which may suggest its involvement in the pathophysiology of the syndrome. Leptin has been shown to stimulate the formation of FGF23 in bones. There is a relationship between the incidence of dyslipidemia, adipose tissue mass and the concentration of fibroblast growth factor 23. The main aim of the presented research project is to assess the concentration of vitamin D, calcium, and selected hormones as well as the concentration of adipokines (leptin) in girls diagnosed with polycystic ovary syndrome.

MATERIALS AND METHODS

The study included a population of 85 girls and young women aged 14 to 22 years. The study group included 37 girls who were diagnosed with polycystic ovary syndrome according to the modified Rotterdam's criteria. The control group consisted of 48 completely healthy girls. In the first stage of the study participants were required to answer background questions. Next, anthropometric measurements were performed. The laboratory tests assessed: leptin, FGF23, FSH, SHGB, total testosterone, DHEA-S, 25-OH-D3, PTH, calcium, androstadiene, AMH, glucose, insulin.

RESULTS

The vitamin D level in the group with polycystic ovary syndrome was lower than in the control group, but there was no statistically significant difference. The level of anti-Müllerian hormone was significantly higher in the group of girls diagnosed with PCOS compared to the control group. Statistically significant differences between both groups were also noted in the HOMA-IR value. The concentration of calcium, parathyroid hormone, FGF23 and leptin in the study and control groups showed no statistically significant difference.

CONCLUSIONS

In the studied group of girls with PCOS, no correlation between the level of vitamin D and selected parameters such as: AMH leptin, HOMA-IR and FGF23 was confirmed. On this basis, it can be assumed that additional vitamin D supplementation would not reduce the symptoms of polycystic ovary syndrome.

Association Between Secondary Hyperparathyroidism and Body Composition in Pediatric Patients With Moderate and Advanced Chronic Kidney Disease

Objective: This single center cross-sectional study aims to investigate the association between secondary hyperparathyroidism and body composition in pediatric patients with moderate (stage 3) and advanced (stage 4-5) chronic kidney disease (CKD). Methods: 61 patients (median age: 13.4 years) were included. Body composition indices, including lean tissue index (LTI) and fat tissue index (FTI), were measured using multi-frequency bio-impedance spectroscopy. Muscle wasting was defined as LTI adjusted to height-age (HA) z-score < -1.65 SD and high adiposity as FTI z-score > 1.65 SD. Serum mineral metabolism parameters, including serum intact parathormone (iPTH), calcium, phosphorus and 25-hydroxyvitamin D, as well as serum leptin were measured in each patient. In advanced CKD patients, the mean values of serum mineral laboratory parameters of the 6 months prior to body composition assessment were recorded, and alfacalcidol index, defined as weekly alfacalcidol dose (mcg/week) per pg/ml of iPTH × 1,000, was calculated. Results: In moderate CKD (31 patients), high iPTH (>90 ng/ml) was observed in 10 (32.3%) patients and was associated with higher FTI z-score (p = 0.022). Moreover, serum iPTH was negatively correlated to LTI HA z-score (rs = -0.486, p = 0.006), and positively correlated to serum leptin levels (rs = 0.369, p = 0.041). The positive correlation between FTI z-score and iPTH (rs = 0.393, p = 0.039) lost significance after adjustment for serum leptin. iPTH was positively associated with high adiposity (12 patients, 38.7%) after adjustment for the other mineral metabolism parameters (OR 1.023, 95% CI 1.002-1.045, p = 0.028). In advanced CKD (30 patients), no significant correlation was observed between iPTH and body composition indices and serum leptin levels. Eleven (36.7%) patients with muscle wasting presented lower alfacalcidol index (p = 0.017). Alfacalcidol index ≤ 24 was strongly associated with muscle wasting after adjustment for CKD stage and other mineral metabolism parameters (OR 7.226, 95% CI 1.150-45.384, p = 0.035). Conclusion: Secondary hyperparathyroidism is associated with high adiposity in moderate but not in advanced CKD, with leptin acting as a potential contributive factor. In advanced CKD, targeting higher alfacalcidol weekly dose per each unit of serum PTH seems beneficial for preventing muscle wasting.

Update on the Crosstalk Between Adipose Tissue and Mineral Balance in General Population and Chronic Kidney Disease

Adipose tissue is nowadays considered as a major endocrine organ, which apart from controlling lipid metabolism, displays a significant role in energy expenditure, food intake and in the regulation of various systemic physiological processes. Adipose derived pro-inflammatory cytokines and adipokines, particularly leptin and adiponectin, provide inter-communication of adipose tissue with various metabolic pathways, ultimately resulting in a complex network of interconnected organ systems. Recent clinical and experimental research has been focused on exploring the direct interaction between adipokine profile and elements of mineral metabolism, including parathormone (PTH), fibroblast growth factor-23 (FGF23) and calcitriol. The emerging crosstalk between adipose tissue and calcium and phosphorus homeostasis suggests that metabolic disorders from one system may directly affect the other and vice versa. It is current knowledge that fat metabolism disturbance, commonly encountered in obese individuals, influences the expression of calciotriopic hormones in general population, while various clinical trials attempting to successfully achieve body fat loss by modulating mineral profile have been published. In chronic kidney disease (CKD) state, there is an increasing evidence suggesting that mineral disorders, influence adipose tissue and linked endocrine function. On the contrary, the impact of disturbed fat metabolism on CKD related mineral disorders has been also evocated in clinical studies. Recognizing the pathogenetic mechanisms of communication between adipose tissue and mineral balance is critical for understanding the effects of metabolic perturbations from the one system to the other and for identifying possible therapeutic targets in case of disrupted homeostasis in one of the two connected systems. To that end, this review aims to enlighten the recent advances regarding the interplay between mineral metabolism, fat mass and adipokine profile, based on in vitro, in vivo and clinical studies, in general population and in the course of CKD.

A molecular circadian clock operates in the parathyroid gland and is disturbed in chronic kidney disease associated bone and mineral disorder

Circadian rhythms in metabolism, hormone secretion, cell cycle and locomotor activity are regulated by a molecular circadian clock with the master clock in the suprachiasmatic nucleus of the central nervous system. However, an internal clock is also expressed in several peripheral tissues. Although about 10% of all genes are regulated by clock machinery an internal molecular circadian clock in the parathyroid glands has not previously been investigated. Parathyroid hormone secretion exhibits a diurnal variation and parathyroid hormone gene promoter contains an E-box like element, a known target of circadian clock proteins. Therefore, we examined whether an internal molecular circadian clock is operating in parathyroid glands, whether it is entrained by feeding and how it responds to chronic kidney disease. As uremia is associated with extreme parathyroid growth and since disturbed circadian rhythm is related to abnormal growth, we examined the expression of parathyroid clock and clock-regulated cell cycle genes in parathyroid glands of normal and uremic rats. Circadian clock genes were found to be rhythmically expressed in normal parathyroid glands and this clock was minimally entrained by feeding. Diurnal regulation of parathyroid glands was next examined. Significant rhythmicity of fibroblast-growth-factor-receptor-1, MafB and Gata3 was found. In uremic rats, deregulation of circadian clock genes and the cell cycle regulators, Cyclin D1, c-Myc, Wee1 and p27, which are influenced by the circadian clock, was found in parathyroid glands as well as the aorta. Thus, a circadian clock operates in parathyroid glands and this clock and downstream cell cycle regulators are disturbed in uremia and may contribute to dysregulated parathyroid proliferation in secondary hyperparathyroidism.

Map and model-moving from observation to prediction in toxicogenomics

BACKGROUND

Chemicals induce compound-specific changes in the transcriptome of an organism (toxicogenomic fingerprints). This provides potential insights about the cellular or physiological responses to chemical exposure and adverse effects, which is needed in assessment of chemical-related hazards or environmental health. In this regard, comparison or connection of different experiments becomes important when interpreting toxicogenomic experiments. Owing to lack of capturing response dynamics, comparability is often limited. In this study, we aim to overcome these constraints.

RESULTS

We developed an experimental design and bioinformatic analysis strategy to infer time- and concentration-resolved toxicogenomic fingerprints. We projected the fingerprints to a universal coordinate system (toxicogenomic universe) based on a self-organizing map of toxicogenomic data retrieved from public databases. Genes clustering together in regions of the map indicate functional relation due to co-expression under chemical exposure. To allow for quantitative description and extrapolation of the gene expression responses we developed a time- and concentration-dependent regression model. We applied the analysis strategy in a microarray case study exposing zebrafish embryos to 3 selected model compounds including 2 cyclooxygenase inhibitors. After identification of key responses in the transcriptome we could compare and characterize their association to developmental, toxicokinetic, and toxicodynamic processes using the parameter estimates for affected gene clusters. Furthermore, we discuss an association of toxicogenomic effects with measured internal concentrations.

CONCLUSIONS

The design and analysis pipeline described here could serve as a blueprint for creating comparable toxicogenomic fingerprints of chemicals. It integrates, aggregates, and models time- and concentration-resolved toxicogenomic data.

Energy-Dense Diets and Mineral Metabolism in the Context of Chronic Kidney Disease⁻Metabolic Bone Disease (CKD-MBD)

The aim of this paper is to review current knowledge about the interactions of energy-dense diets and mineral metabolism in the context of chronic kidney disease–metabolic bone disease (CKD-MBD). Energy dense-diets promote obesity and type II diabetes, two well-known causes of CKD. Conversely, these diets may help to prevent weight loss, which is associated with increased mortality in advanced CKD patients. Recent evidence indicates that, in addition to its nephrotoxic potential, energy-dense food promotes changes in mineral metabolism that are clearly detrimental in the context of CKD-MBD, such as phosphorus (P) retention, increased concentrations of fibroblast growth factor 23, decreased levels of renal klotho, and reduction in circulating concentrations of calcitriol. Moreover, in uremic animals, a high fat diet induces oxidative stress that potentiates high P-induced vascular calcification, and these extraskeletal calcifications can be ameliorated by oral supplementation of vitamin E. In conclusion, although energy-dense foods may have a role in preventing undernutrition and weight loss in a small section of the CKD population, in general, they should be discouraged in patients with renal disease, due to their impact on P load and oxidative stress.

Hypocaloric Diet Prevents the Decrease in FGF21 Elicited by High Phosphorus Intake

The effect of dietary phosphorus (P) on fibroblast growth factor 21 (FGF21)/β-klotho axis was investigated in rats that were fed diets with: Normal (NP) or high P (HP) and either normal (NC), high (HC) or low calories (LC). Sampling was performed at 1, 4 and 7 months. Plasma FGF21 concentrations were higher (p < 0.05) in NC and HC than in LC groups. Increasing P intake had differing effects on plasma FGF21 in rats fed NC and HC vs. rats fed LC at the three sampling times. When compared with the NP groups, FGF21 concentrations decreased at the three sampling points in rats fed NC-HP (80 vs. 194, 185 vs. 382, 145 vs. 403 pg/mL) and HC-HP (90 vs. 190, 173 vs. 353, 94 vs. 434 pg/mL). However, FGF21 did not decrease in rats fed LC-HP (34 vs. 20, 332 vs. 164 and 155 vs. 81 pg/mL). In addition, LC groups had a much lower liver FGF21 messenger ribonucleic acid/glyceraldehyde 3-phosphate dehydrogenase (mRNA/GAPDH) ratio (0.51 ± 0.08 and 0.56 ± 0.07) than the NC-NP (0.97 ± 0.14) and HC-NP (0.97 ± 0.22) groups. Increasing P intake reduced liver FGF21 mRNA/GAPDH in rats fed NC and HC to 0.42 ± 0.05 and 0.37 ± 0.04. Liver β-klotho mRNA/GAPDH ratio was lower (p < 0.05) in LC groups (0.66 ± 0.06 and 0.59 ± 0.10) than in NC (1.09 ± 0.17 and 1.03 ± 0.14) and HC (1.19 ± 0.12 and 1.34 ± 0.19) groups. A reduction (p < 0.05) in β-klotho protein/α-tubulin ratio was also observed in LC groups (0.65 ± 0.05 and 0.49 ± 0.08) when compared with NC (1.12 ± 0.11 and 0.91 ± 0.11) and HC (0.93 ± 0.17 and 0.87 ± 0.09) groups. In conclusion β-klotho is potently regulated by caloric restriction but not by increasing P intake while FGF21 is regulated by both caloric restriction and increased P intake. Moreover, increased P intake has a differential effect on FGF21 in calorie repleted and calorie depleted rats.

Effect of cardiometabolic risk factors on the relationship between adiposity and bone mass in girls

BACKGROUND/OBJECTIVE

Childhood obesity has been separately associated with cardiometabolic risk factors (CMRs) and increased risk of fracture. However, both augmented and compromised bone mass have been reported among overweight/obese children. Metabolic dysfunction, often co-existing with obesity, may explain the discrepancy in previous studies. The aim of this study was to examine whether the relationship between adiposity and dual-energy X-ray absorptiometry (DXA) derived bone mass differed in young girls with and without CMR(s).

SUBJECTS/METHODS

Whole-body bone and body composition measures by DXA and measures of CMR (fasting glucose, high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), systolic and diastolic blood pressure, waist circumference (WC)) were obtained from 307, 9- to 12-year-old girls. Girls with 1 or ≥ 2 CMR(s) were considered to be at risk (vs. no CMR). Multiple linear regression was used to test the relationship of total fat mass with total body bone mineral content (BMC) after controlling for height, lean mass, CMR risk, and other potential confounders.

RESULTS

There was a significant interaction between CMR risk and total body fat mass. When girls were stratified by CMR group, all groups had a significant positive relationship between fat mass and BMC (p < 0.05), however, girls with ≥ 2 CMRs had a lower BMC for a given level of body fat. Total body fat was not significantly related to bone mineral density (p > 0.05).

CONCLUSION

Fat mass has a positive relationship with BMC even after controlling for lean mass. However, the positive relationship of fat mass with BMC may be attenuated if multiple CMRs are present.

Parathyroid hormone in surgery-induced weight loss: no glucometabolic effects but potential adaptive response to skeletal loading

PURPOSE

Increased parathyroid hormone (PTH) is commonly associated with obesity, and its role in the pathogenesis of obesity-related glucometabolic abnormalities is uncertain. We aimed to explore the relationships of PTH with glucose/insulin homeostasis parameters before and after bariatric surgery-induced weight loss, and whether they depend or not on 25-hydroxyvitamin D (25OHD) status.

METHODS

We included 42 subjects (27 women, aged 40 ± 5 years, BMI 48.5 ± 7.3 kg/m²) without diabetes, chronic kidney disease, or hyperparathyroidism undergoing sleeve gastrectomy. The following parameters were evaluated before and 6 months after surgery: circulating levels of PTH, calcium, phosphorus, 25OHD, leptin, insulin growth factor (IGF)-1; 75-g oral glucose tolerance test to derive measures of insulin sensitivity (ISI) and secretion (Stumvoll index); dual-energy X-ray absorptiometry to assess fat distribution and bone mineral density.

RESULTS

Weight loss was accompanied by significant reduction of PTH levels (77.9 ± 19.1 vs. 60.5 ± 13.4 pg/ml; p = 0.005), without concomitant modification of 25OHD status. Both baseline PTH and its postoperative percent change resulted associated, with baseline fat mass (β = 0.615, p = 0.003) and its concurrent postoperative reduction (r = 0.419; p = 0.006), but neither with glucose homeostasis parameters nor their respective variations after weight loss. Interestingly, leptin reduction after weight loss was independently related to PTH change (β = 0.396, p = 0.015) and IGF-1 levels (β = 0.176, p = 0.059).

CONCLUSIONS

Circulating PTH decreases with fat mass reduction independent of 25OHD status, but it  is not associated with improvement of insulin resistance and related metabolic parameters. Leptin and PTH may mediate the cross-talk between adipose tissue and parathyroid glands, which possibly contributes to bone adaptation to excess body weight.

The intriguing connections of leptin to hyperparathyroidism

PURPOSE

Leptin has been implicated in bone metabolism, but the association with parathyroid gland function has not been fully clarified. This review aimed to summarize evidence of the association between leptin and hyperparathyroidism, both primary and secondary, elucidating the potential pathophysiologic and therapeutic consequences between leptin and parathyroid hormone, hopefully prompting the design of new studies.

RESULTS

Experimental studies indicate a positive loop between leptin and parathyroid hormone in primary hyperparathyroidism. Dissimilar, parathyroid hormone seems to inhibit leptin expression in severe secondary hyperparathyroidism. Data from clinical studies indicate higher leptin levels in patients with primary hyperparathyroidism than controls, but no association between parathyroid hormone and leptin levels, as well as a minimal or neutral effect of parathyroidectomy on leptin levels in patients with primary hyperparathyroidism. Clinical data on secondary hyperparathyroidism, mainly derived from patients with chronic kidney disease, indicate a potential inverse association between leptin and parathyroid hormone in some, but not all studies. This relationship may be affected by the diversity of morbidity among these patients.

CONCLUSIONS

Data from experimental studies suggest a different association between leptin and parathyroid hormone in primary and secondary hyperparathyroidism. Data from clinical studies are conflicting and potentially affected by confounders. More focused, well-designed studies are warranted to elucidate a potential association between leptin and parathyroid hormone, which may have specific clinical implications, i.e., targeting obesity and hyperleptinemia in patients with hyperparathyroidism.